User's Manual

SATELLINE-3AS

User Guide, Version 2.2

5 TRANSPARENT DATA TRANSMISSION

5.1 Serial interface, data format

The SATELLINE-3AS radio modem serial interface uses an asynchronous data format. No

external synchronising signal is needed, since necessary timing information is acquired from the

start and stop bits transmitted before and after each data field bits (byte).

The data transfer speed of the serial interfaces can be set to 300, 600, 1200, 2400, 4800,

9600, 19200 or 38400 bps (b

bits p

per s

second). The length of the data field must be 7, 8 or 9

bits. When using a data field length of 7 or 8 bits, a parity bit may also be used.

One character to be transmitted will thus contain a start bit; the data bits (which define the

specific character in question); an optional parity bit and one or two stop bits. The overall length

of one character is therefore 10, 11 or 12 bits. This should be taken into account when

calculating the data throughput capability of a system. In other words, the number of start, stop

and parity bits must be considered. A useful rule of thumb is that at a data transfer speed of

9600 bps, the transmission of one character will require roughly one millisecond (1 ms).

Start Data Parity End

Asynchronous character data format

Example:

Example:Example:

Example: With an 8-bit data character length and taking, for example, a decimal value of

”204”, (which corresponds to a binary value of ”11001100”) and with a start bit value of ”0”,

parity bit set to either “NO” (NONE), ”0” or ”1” and with a stop bit value of ”1”, the possible

combinations are listed in the table below:

DATA FORMAT CHARACTER CHARACTER LENGTH

8 bit, no parity, 1 stop bit 0110011001 10 bit

8 bit, even parity, 1 stop bit 01100110001 11 bit

8 bit, odd parity, 1 stop bit 01100110011 11 bit

8 bit, no parity, 2 stop bits 01100110011 11 bit

8 bit, even parity, 2 stop bits 011001100011 12 bit

8 bit, odd parity, 2 stop bits 011001100111 12 bit

If the settings of data speed, character length, parity or the number of stop bits differ between

the radio modem and the terminal, errors will be introduced into the transferred data. The serial

port settings of each individual radio modem in a system can all be different apart from the data

length setting (7, 8 or 9 bits), which must always be the same in each individual radio data

modem. In other words, the serial port used, the data transfer speed, parity and number of stop

bits, can be different in different parts of a same system. This is especially useful where one part

of the system uses an RS-485 serial port and another part uses the RS-232 serial port. In other

words, radio modems may also be utilised as serial port adapters in addition to the more

common role of wireless data transfer.

The serial port settings can be changed in the Programming Mode.